1. Field of the Invention
The present invention relates to a recording head that has a buffer chamber, and ejects ink.
2. Description of the Related Art
An image forming apparatus that forms an image on a recording medium, has a recording head provided with an ejection port that ejects ink. In recent years, images with a high quality and a high definition have been increasingly demanded, and in order to realize such images, the ejection ports of the recording heads are highly-miniaturized and have higher density. In addition, a refill frequency representing a cycle from ink ejection to the next ink ejection is set at a high level. However, if the ejection port of the recording head is highly-miniaturized, and the refill frequency is set at a high level, a great meniscus oscillation of the ink is likely to be generated at the ejection port. The great meniscus oscillation causes poor printing of images to be formed on a recording medium.
A recording head including a chip unit (recording head unit) where an ejection portion is formed, a tank holder unit that holds an ink tank, a liquid flow path forming member including a flow path, and an elastic material for sealing a liquid supply port is discussed in Japanese Patent Application Laid-Open No. 2004-122463. The tank holder unit and the flow path forming member are joined together, and a main flow path (communication passage) and a buffer chamber provided on one end portion of the main flow path are formed on a joint surface. Specifically, the buffer chamber is constructed mainly by a recessed portion of the flow path forming member which is formed on the joint surface between the tank holder unit and the flow path. Then, the buffer chamber is integrated with a through-hole that penetrates the flow path forming member. By having a gas encapsulated in advance within the buffer chamber, a pressure oscillation generated by ejection of the ink from the ejection port of the recording head, is absorbed by contraction of the gas within the buffer chamber. As a result, a meniscus oscillation is hardly generated.
At the time of the manufacture of the recording head, by running a cleaning water from the buffer chamber through the through-hole integrated with it prior to joining the recording head and the chip unit, the buffer chamber can be easily and surely cleaned. In other words, it is possible to wash out foreign matters that happen to be mixed into the buffer chamber in the course of manufacturing process of the recording head. Accordingly, a frequency of clogging the ejection port and defective ejection of the inks can be suppressed, even when foreign matters are mixed into the liquid supply path through the main flow path from the buffer chamber and carried to the ejection port after the completion of the recording head. Because the through-hole integrated with the buffer chamber is blocked when the chip unit and the flow path forming member are joined, there is no need to add a step for blocking the through-hole. Specifically, since the through-hole is blocked by the elastic material sealing a liquid supply port arranged between the flow path forming member and the chip unit, leakage of the ink from the through-hole is suppressed.
However, as illustrated in FIGS. 9A to 9C, when the recording head ejects the ink onto the recording medium, ink within a liquid supply path may flow into the buffer chamber after ejection of the ink and is pushed back by the gas within the buffer chamber. At that time, air bubbles may be added to the ink. If the gas within the buffer chamber expands to push back against the air bubbles together with the ink, gas-liquid exchange may be caused and the air bubbles enter into the liquid supply path from the main flow path. In such a case, pressure generated for ejecting the ink may be possibly absorbed by the air bubbles. In addition, the air bubbles instead of the ink may be discharged from the ejection port, thereby ink omission may possibly occur in images to be formed.
In the configuration of the recording head discussed in Japanese Patent Application Laid-Open No. 2004-122463, when the recording head ejects ink onto a recording medium, a port communicating with the through-hole of the buffer chamber is located at a bottom surface (lower side in a vertical direction) of the buffer chamber. In such a configuration, in a state where the ink is flowing into the buffer chamber, the ink enters into the through-hole through the communication port located at the bottom surface of the buffer chamber, so that the gas within the through-hole forms air bubbles in the vicinity of the communication port within the buffer chamber. By the oscillation of the recording medium during image formation, the air bubbles may possibly enter into the main flow path from the buffer, and remain within the main flow path. If the air bubbles remain within the main flow path, the air bubbles may move to the liquid supply path, while flowing into and discharging from the buffer chamber of the ink by the meniscus oscillation are repeated. Thus, the air bubbles enter into the liquid supply path and ink omission occurs in images to be formed.